Deformable articulating templates

ABSTRACT

A method for generating a patient-specific prosthetic implant is disclosed which includes generating, using one or more processors from a medical image of a human anatomical feature, a three dimensional electronic representation of the human anatomical feature including size and surface curvature features matching the human anatomical feature, the surface curvature features including one or more radii of curvature on an outer camming surface of the human anatomical feature. A prosthetic implant template is selected, using the one or more processors, from a database of prosthetic implant templates, and the custom implant is virtually designed to imitate the size and surface curvature features of the three dimensional electronic representation based on the selected prosthetic implant template. Fit of the custom implant is tested, virtually using the one or more processors, using the three dimensional electronic representation of the human anatomical feature.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/640,082 filed Mar. 6, 2015, which is a divisional of U.S.patent application Ser. No. 13/203,012 filed Feb. 25, 2010, which is anational phase entry application of International PCT Patent ApplicationNo. PCUS2010/25466 filed Aug. 24, 2011, which claims the benefit of U.S.Provisional Patent Application Ser. No. 61/208,509 filed. Feb. 25, 2009and U.S. Provisional Patent Application Ser. No. 61/222,560, filed Jul.2, 2009, the disclosure of each of which is hereby incorporated hereinby reference.

TECHNICAL

The present disclosure relates to orthopaedic implants and, morespecifically, to methods and devices utilized to design orthopaedicimplants and orthopaedic jigs for use with joint replacement andrevision procedures.

INTRODUCTION TO THE INVENTION

Of primary interest to the knee prosthetics industry is the analysis ofthe intrinsic shape differences of the knee joint between differentethnic populations for development of implantable orthopaedic devices.The study presented is thus three-fold: by developing a novel automaticfeature detection algorithm, a set of automated measurements can hedefined based on highly morphometric variant regions, which then allowsfor a statistical framework when analyzing different populations' kneejoint differences.

Ethnic differences in lower limb morphology focuses on the differencesbetween Asian and Western populations because this variation is of greatimport in implant design. For example, Chinese femora are moreanteriorly bowed and externally rotated with smaller intermedullarycanals and smaller distal condyles than Caucasian femora. Likewise,Caucasian femora are larger than Japanese femora in terms of length anddistal condyle dimensions. Ethnic differences in proximal femur bonemineral density (BMD) and hip axis length also exists between AmericanBlacks and Whites. The combined effects of higher BMD, shorter hip axislength, and shorter intertrochanteric width may explain the lowerprevalence of osteoporotic fractures in Black women compared to theirWhite counterparts. Similarly, elderly Asian and Black men have beenfound to have thicker cortices and higher BMD than White and Hispanicmen, which may contribute to greater bone strength in these ethnicgroups. In general, Blacks have thicker bone cortices, narrowerendosteal diameters, and greater BMD than Whites. Interestingly, though,these traits are most pronounced in African Blacks compared to AmericanBlacks.

The following analysis considers metric and geometric morphometricvariation in the lower limb of modern American Blacks, Whites and EastAsians. Three-dimensional statistical bone atlases are used in order tofacilitate rapid and accurate data collection in the form of automatedmeasurements, as well as measurements used in biomedical studies andsome newly-devised measurements. The shape analysis is conducted with astatistical treatment combining Principal Components Analysis (PCA) andMultiple Discriminant Analysis; metric analysis is performed usingt-tests, power tests, and linear discriminant analysis in the ImplantDesign and Analysis Suite (see co-pending U.S. patent application Ser.No. 12/673,640, entitled, IMPLANT DESIGN ANALYSIS SUITE, the disclosureof which is incorporated herein by reference) system. The results ofthese analyses add to the existing knowledge of morphological variationin the knee joint and provide useful information that can be extractedfor knee prosthesis design as will be outlined in the remainder of thisdisclosure.

The innovativeness of the instant approach derives, in part, from theuse of Computed Tomography (CT) scans for data collection combined withthe computational power and precision offered by statistical boneatlases. An exemplary data set that comprises 943 male and femaleindividuals (81.5% American White, 9% American Black and 9.5% EastAsians, where the overall male/female ratio 65/35%) was scanned using CTscans. Only normal femora and tibia were included in this study; femoraor tibia with severe osteophytes and other abnormalities werespecifically excluded. Only one femur and tibia was chosen from eachindividual, with no preference taken to either right or left side.

The bones were CT scanned using 0.625 mm×0.625 mm×0.625 mm cubic voxels.The result is high resolution, three dimensional radiographs in the formof DICOM image slices. This stacked image data was then segmented andsurface models were generated. This process has been found to bereliable with negligible inter- and intra-observer error. These modelswere then added to the ethnicity-specific statistical bone atlases.

Briefly, a bone atlas is an average mold, or template mesh, thatcaptures the primary shape variation of a bone and allows for thecomparison of global shape differences between groups or populations.Bone atlases were developed initially for automatic medical imagesegmentation; however, it can be used as a way to digitally recreate abone and conduct statistical shape analyses. In addition, bone atlaseshave proven useful in biological anthropology as a means of studyingsexual dimorphism and for reconstructing hominid fossils and makingshape comparisons among fossil species.

For the ethnicity difference analysis, a previously developed techniquefor creating a statistical representation of bone shape was employed ina novel manner. Three separate statistical atlases of femora werecompiled with one atlas containing only American White femora, one atlascontaining only American Black femora, and one atlas containing onlyEast Asian femora. Likewise, three separate atlases were created for thetibia and divided in the same manner (i.e., American White, Black tibiaeand East Asians). The processes of creating these statistical atlasesand adding bones to the atlases are outlined hereafter.

First, all of the bone models in the dataset were compared, and a bonemodel with average shape characteristics was selected to act as atemplate mesh. The points in the template mesh were then matched tocorresponding points in all of the other training models. This ensuresthat all of the bones have the same number of vertices and the sametriangular connectivity. Next, a series of registration and warpingtechniques was used to select corresponding points on all the other bonemodels in the training set. This process of picking pointcorrespondences on new models to be added to the atlas is ‘non-trivial’.The matching algorithm described hereafter uses several well-knowntechniques of computer vision, as well as a novel contribution for finalsurface alignment.

During the first step in the matching algorithm, the centroids of thetemplate mesh and the new mesh were aligned, and the template mesh waspre-scaled to match the bounding box dimensions of the new mesh. Second,a rigid alignment of the template mesh to the new mesh was performedusing a standard vertex-to-vertex Iterative Closest Point (ICP)algorithm. Third, after rigid alignment, a general affine transformationwas performed without iteration. This method was applied to align thetemplate mesh to the new mesh using 12 degrees of freedom (includingrotations, translations, scaling, and shear). After the affinetransformation step, the template and new model have reached the limitsof linear transformation, but local portions of the models still remainsignificantly distant. Since the goal of final surface-to-surfacematching is to create new points on the surface of the new model thatwill have similar local spatial characteristics as the template model, anovel non-linear iterative warping approach was developed to reducemisalignment.

Referring to FIG. 1, to achieve point correspondence, an iterativealgorithm is used where the closest vertex-to-vertex correspondences arefound from the template to the new model as before, but now thecorrespondences from the new model to the template model are also found.Using both of these point correspondences, points on the template meshare moved toward locations on the new mesh using a non-symmetricweighting of the vectors of correspondence. Next, a subroutineconsisting of an iterative smoothing algorithm is applied to thenow-deformed template mesh. This smoothing algorithm seeks to averagethe size of adjacent triangles on the template mesh, thereby eliminatingdiscontinuities. At the beginning of the warping algorithm, thesmoothing algorithm uses the actual areas of the surrounding trianglesto dictate the smoothing vector applied to each point, which aids ineffectively removing outlying points with large triangles. Consequently,at the beginning of the process, the template mesh makes large steps,and larger smoothing is required. Toward the end of the process,however, the smoothing vector is normalized by the total area of thesurrounding triangles, which allows for greater expansion of thetemplate mesh into areas of high curvature. After this procedure hasbeen completed on all the femora and tibiae in their respective atlases,the atlases are ready for morphological shape analyses and automatedmetric comparisons.

An innovative statistical treatment was used to analyze global shapedifferences between the two groups. This method utilizes the power of(linear and nonlinear) PCA both as a means of variable reduction and asa global shape descriptor. This method is designed to find points ofhigh discrimination between different gender and/or different ethnicgroups when normalized against the first principal component (PC), whichis considered primarily to scale. This procedure highlights areas onmodels that would be highly discriminating without the use of any otherinformation. The landmarks identified by this algorithm provide adequatediscrimination without the use of any other landmarks between ethnicgroups. This feature finder algorithm is used to examine femoral andtibial shape differences independent of the size differences betweenAmerican Whites, Blacks and East Asians.

A wide array of comparisons was made using specific measurements atdefined landmarks on the ethnicity-specific statistical atlases. Theselandmarks were chosen based on surgical importance, clinical relevance,and historical measurements. Since the atlas consists of homologouspoints on each femur or tibia model, it provides ample information forautomating this process. Also, each bone model in the atlas is alignedto the same coordinate frame. A total of 99 femur and 23 tibiameasurements, angles, and indices were calculated. Furthermore, forpurposes of brevity, only the most significant metric properties arediscussed in the results section. Unless otherwise specified, themeasurements outlined below represent three dimensional (3D) Euclideandistances between pairs of landmarks, and angles are measured as 3Drotations between vectors. In some instances these measurements wereprojected onto a plane for comparison with previous work in the field. Asubset of these measurements is shown in FIGS. 2-4. The landmarks thatdefine the measurement endpoints are first computed and then definedrelative to surgical and anatomical axes.

Presented are novel methods to ascertain ethnic differences on thedistal femur and proximal tibia on a global scale, to discover regionsthat were likely to offer discriminating information, and to measurerelevant surgical and anatomical features to aid implanted prosthesisdesign. Different studies have tried to identify ethnical differences ofthe femur and tibia using measurement techniques that lacked accuracy orprecision. Unfortunately, these methods have been unable to findfeatures of smaller consequence.

The ordered series of methods used pursuant to the instant disclosureevidenced significant global differences among sex and race, whichsubsequently allowed for isolation of regions likely to be highlydifferent using the feature finder method, and finally allowed for thecoding of algorithms to locate and measure surgically relevant anatomicfeatures with a high degree of accuracy and repeatability. Bones withdifferent scales were considered to have the possibility of shapechanges dependent on size. In this way, correlations between measuredvariables and size were removed in order to expose demonstrable shapedifferences inherent to the ethnicities.

The inventor has used the foregoing analysis to determine that AmericanBlacks have longer, straighter femora with narrower knees than AmericanWhites. In addition, this analysis revealed differences in thedimensions and orientation of the lateral condyle that result in overallshape differences in the distal femur: American Blacks have atrapezoidal-shaped knee, and American Whites have a more square-shapedknee. For each group, the differences in the distal femur are echoed inthe adjacent tibia, whereby American Blacks have a longer lateral tibialcondyle. The mean medial-lateral length of the tibial plateau isslightly longer in Blacks than in Whites, but this difference was notoverly significant given the sample size. However, American Blacks dohave significantly longer and more robust tibiae. In this study, majorshape difference was found between East Asian population and bothAmerican whites and American blacks.

It is not clear to what extent genetic differences contribute to lowerlimb morphology, admixed individuals present a challenge. Indeed, bloodtype data indicates that since their arrival in the United States,American Blacks have become more similar to American Whites and moredivergent from their ancestral West African population.

Although racial differences in lower limb morphology are apparent andregister statistically significant, there may be more statistical noisein the American Black sample versus the American White sample. Thisnoise may be a result of the combined effects of genetic admixture sincetheir arrival in the United States, as well as relaxed selection in amore temperate environment. Nonetheless, as discussed earlier, theeffects of admixture have not erased the distinctive morphologicaldifferences between these subgroups of the American population.

In order, to understand normal knee joint kinematics, one must firstunderstand the anatomy of the articulating surfaces of the knee joint.The knee joint is the articulation of the two largest bones in the humanlower extremity, the tibia and the femur. The articular surfaces at theknee joint consists of the curved surfaces that form the lateral andmedial condyles of the distal portion of the femur and are in contactwith the lateral and medial tibial plateaus of the proximal portion ofthe tibia.

The femoral condyles blend into an anterior groove, the trochlea, whichis the articulation for the patella or kneecap. The tibial plateaus areseparated by an intercondylar eminence, which serves as an attachmentpoint for the anterior cruciate ligament and the menisci. The tibialplateaus are also asymmetric, with the lateral plateau the smaller ofthe two. Anatomical studies of the femorotibial articulation have shownthat the medial compartment has greater contact area than the lateralcompartment.

The fibula is attached to the tibia's lateral side by a dense membranealong its length and at the ends by cartilaginous joints supported byligaments. The connection of the bones permits very little relativemovement. The proximal tibia-fibular joint is below the level of thetibia-femoral articulation, while the distal ends of the two bones formthe proximal end of the ankle joint.

In the normal knee, posterior femoral rollback during an increasingflexion routinely occurs. Greater amounts of posterior femoral rollbackhave been observed during activities requiring greater magnitudes offlexion such as a deep knee bend maneuver. Posterior rollback issubstantially greater at the lateral femorotibial articulation thanmedially, therefore creating a medial pivot type of axial rotationalpattern in which the tibia internally rotates relative to the femur asflexion increases. Numerous kinematic evaluations have found a similarpattern and magnitude of posterior femoral rollback during deep flexionactivities. This differs somewhat from axial rotational patternsobserved after total knee arthroplasty (TKA), which showed lowermagnitudes of axial rotation and occasional pathologic rotationalpatterns such as lateral pivot rotation and reverse screw-home rotation(tibia externally rotating relative to the femur with increasingflexion).

Also, the anterior translation of the femur on the tibia observed afterTKA has numerous potential negative consequences. First, anteriorfemoral translation results in a more anterior axis of flexion,lessening maximum knee flexion. Second, the quadriceps moment arm isdecreased, resulting in reduced quadriceps efficiency. Third, anteriorsliding of the femoral component on the tibial polyethylene (PE) surfacerisks accelerated PE wear.

A primary objective of TKA should be to reproduce the kinematics of anormal knee. At present, this objective is largely overlooked. Numerousin vivo, weightbearing, and fluoroscopic analyses have shown that normalknee kinematics are difficult to obtain after TKA using existingorthopaedic implants. Multiple kinematic abnormalities (reducedposterior femoral rollback, paradoxical anterior femoral translation,reverse axial rotational patterns, and femoral condylar lift-off) arecommonly present. Understanding these kinematic variances assisted indesign of better TKA implants, which work toward reducing andeliminating these kinematic abnormalities or at least accommodating themwithout creating adverse conditions that limit implant performance orlongevity. Most of the knee implants are off-the shelve-knee systems,which are designed for average motion—not patient specific kinematics.Accordingly, TKA motion and kinematics of the knee that areindistinguishable from a normal knee should utilize customization foreach patient. Currently, customization is a difficult task, but theinstant disclosure addresses this customization, in part, by offering adeformable articulating template (DAT) methodology described hereafter.

For purposes of the instant disclosure, radius of curvature is theradius of a circle having a circumferential curvature that approximatesthe curvature of a rounded object. For example, the radius of curvatureis infinite for a straight line, while the radius of decreases frominfinity as the curvature increases. As can be seen in FIG. 5, theradius of curvature for the smaller circle is less than the radius ofcurvature for the larger circle because the curvature of the smallercircle is greater than the curvature of the larger circle. Simply put,the smaller the radius of curvature, the larger the curvature.

Referring to FIGS. 6 and 7, the inventor has found that one may map andsimulate the curvature of the natural knee condyles by applying two ormore radii of curvature along the camming surfaces from anterior toposterior. In particular, it has been found that for the Caucasianpopulation, five distinct radii of curvature (identified as r1-r5)closely track the curvature of the camming surfaces of the condyles fromanterior to posterior. Moreover, it has been found that asymmetry in theradii of the curvature of the condyles is responsible for imposing aninternal rotation of the tibia with respect to the femur during flexion.Beyond 20° of flexion, sliding motion begins on both condyles.

Extension of the knee joint produces a coupled external rotation of thetibia with respect to the femur; this rotation has been described as the“screw-home” movement of the knee. This screw-home movement is due tothe existence of a larger area of bearing surface on the medial condylethan on the lateral condyle. When the whole articular surface of thelateral condyle has been used up, the femur rotates around the tibialspine until the joint is screwed home or close packed in extension. Asthe knee joint flexes and extends, this rotation causes the tibialmotion on the femur to assume a spiral or helicoid form that resultsfrom the anatomical configuration of the medial femoral condyle. As thetibia slides on the femur from the fully extended position, it descendsand ascends the curves of the medial femoral condyle and simultaneouslyrotates externally. This motion is reversed as the tibia moves back intothe fully flexed position. The screw-home mechanism gives more stabilityto the knee in any position than would be possible if the femorotibialjoint was a pure hinge joint.

Referring to FIG. 8, the meniscal cartilages (menisci) between thefemoral condyles and the tibial articular surfaces are two crescenticfibrocartilage structures that serve to deepen the articular surfaces ofthe tibia for reception of the femoral condyles. On cross-section, themenisci have a wedge-like appearance. The menisci perform severalimportant functions, including (1) load transmission across the joint,(2) enhancement of articular conformity, (3) distribution of thesynovial fluid across the articular surface, and (4) prevention of honeimpingement during joint motion. When the menisci are present, theload-bearing area for each condyle approximates 6 cm², but this surfacearea decreases to approximately 2 cm² when the menisci are damaged orseverely degraded. Therefore, when the effective area of load bearing isincreased, the stress transferred to the cartilages is reduced and viceversa.

Referencing FIGS. 9 and 10, in the normal knee joint, the anteriorcruciate ligament (ACL) and the posterior cruciate ligament (PCL) areintrinsic, lying inside the joint in the intercondylar space. Theseligaments control the anteriorpostrior and axial rotational motion inthe joint. The anterior cruciate ligament provides the primary restraintfor anterior movement of the tibia relative to the femur while theposterior cruciate ligament offers the primary restraint to posteriormovement of the tibia, accounting for over 90% of the total resistanceto this movement. FIG. 10 shows the change in length of the ACL and PCLduring different flexion angles of the knee joint. A detaileddescription of the effect of ACL and PCL constraints on the design ofposterior stabilized knee implants will be discussed in more detailhereafter.

The morphologic shape of the distal femur should dictate the shape,orientation, and kinematics of the prosthetic replacement used for TKA.Traditional prosthetic designs incorporate symmetric femoral condyleswith a centered trochlear groove. Traditional surgical techniques centerthe femoral component to the distal femur and position it relative tovariable bone landmarks. However, documented failure patterns andkinematic studies demonstrate how traditional design and surgicaltechniques reflect a poor understanding of distal femoral morphology andknee joint kinematics, in addition to a disregard for the patella andits tracking of the distal femur.

The trochlea is designed to guide and hold the patella. Patella trackingis influenced by many different factors: the geometry of the trochleargroove, the geometry of the posterior side of the patella, soft tissueextensor mechanism and the orientation of the tibia. The normal movementof the patella on the femur during flexion is a vertical displacementalong the central groove of the femoral patellar surface down theintercondylar notch. The geometry of the trochlear groove and theposterior side of the patella constrains patella tracking, particularlyat high flexion angles. The patella is held centrally by the conformityof the facets with the sulcus of the femur and by the patellofemoralligaments. These ligaments represent a conformation of the capsule intothickened structures on the medial and lateral side of the patella.These ligaments are located superiorly and inferiorly on either side,and extend from the anterior surface of the patella posteriorly to theside of each femoral condyle. These ligaments also constrain the motionof the patella, but can be overruled by the sulcus constraints or byexternal forces. In a normal knee it is acceptable to presume that thetracking of the patella will be very similar to the orientation of thetrochlea. As a result, the orientation of the trochlear groove of a kneeprosthesis should be similar to the orientation of the natural trochleato reproduce this natural patella track.

In sum, the knee joint is an example of very well balanced system. Aslight change within this system, affects the whole system. Changeswithin the patella-femoral joint can have considerable long termeffects, as the transmitted forces within this part of the knee jointare relatively high. TKA easily induces changes within thepatella-femoral joint. At present, the simulated trochlear grooveorientation of TKA components does not conform to the natural trochlearorientation. Accordingly, the groove orientation of future femoralcomponents should incorporate a trochlear groove that simulates thenatural orientation of the trochlear groove of a natural femur.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart outlining the process of atlas creation.

FIG. 2 is a screen shot and associated image showing automaticcalculation of landmarks using the IDAS software.

FIG. 3 is a distal end view of a femur showing the axes, landmarks, andmeasurements taken.

FIG. 4 is a frontal view of the femur of FIG. 3, showing certain axes,landmarks, and measurements taken.

FIG. 5 is an exemplary diagram showing how curvature on the surface of abone may be approximated using circles having different radii.

FIG. 6 is a profile view of the lateral condyle of a human knee jointhaving five radii of curvature applied to approximate the curvature ofthe camming surfaces from anterior to posterior.

FIG. 7 is a profile view of the medial condyle of a human knee jointhaving five radii of curvature applied to approximate the curvature ofthe camming surfaces from anterior to posterior.

FIG. 8 is a plan view of the proximal end of a human tibia that includescartilage forming a portion of a human knee joint.

FIG. 9 is a frontal view of a knee joint showing the anterior cruciateligament and posterior cruciate ligament during partial knee flexion.

FIG. 10 includes a series of frontal views of a knee joint at variousdegrees of knee flexion showing the position of the anterior cruciateligament and the posterior cruciate ligament.

FIG. 11 is an overall schematic of an exemplary process for designing anorthopaedic implant that is customized for a patient or comprises one ofa series of templates for general populations.

FIG. 12 is a bottom view of several electronic 3D distal femur modelsgenerated from medical imaging equipment that correspond to actualnatural femurs from human patients.

FIG. 13 is an electronic model of a human knee joint, includingcartilage and ligaments, based upon medical imaging equipment data of anactual human knee joint, with the joint shown in the flexed position.

FIG. 14 is an electronic model of a human knee joint, includingcartilage and ligaments, based upon medical imaging equipment data of anactual human knee joint, with the joint shown proximate full extension.

FIG. 15 is a series of 2D vertical slice representations of a knee jointshowing the interaction between the tibia, femur, and patella proximatefull extension.

FIG. 16 is a 3D representation of the 2D slices of FIG. 15 in additionto other vertical slices to show where the slices are taken and therelative positions of the tibia, femur, and patella proximate fullextension.

FIG. 17 is a distal view of the femur showing furthest anterior, distaland posterior points along the medial and lateral camming paths.

FIG. 18 is a compilation of views of the medial and lateral condyles ofa distal femur having a path approximating the most outward portion ofthe camming surface of each condyle throughout the range of motion ofeach condyle.

FIG. 19 is an elevated posterior view of a 3D representation showing atibia and patella relative to the path of the outward most portion ofthe camming surface of each condyle for an exemplary distal femur, aswell as the inner most surface of the trochlear groove associated withthe distal femur.

FIG. 20 is a lateral profile view of a knee joint showing the tibia andpatella of FIG. 18, as well as the camming paths and trochlear groovepath, in addition to showing the distal femur in phantom.

FIG. 21 is an exemplary chart representing measurements of radii ofcurvature for a series of distal femurs for both human males andfemales, as well as where the measurements were taken.

FIG. 22 is a lateral profile view of a knee joint showing the tibia andpatella relative to the positions and size of corresponding radii ofcurvature for the outermost camming surface paths of the lateral andmedial condyles.

FIG. 23 is a frontal view showing a common differences between the shapeof a distal femur among Asians, American Whites, and American Blacks.

FIG. 24 is a profile view showing a common differences between the shapeof a medial femoral condyle among Asians, American Whites, and AmericanBlacks.

FIG. 25 is a profile view showing a common differences between the shapeof a lateral femoral condyle among Asians, American Whites, and AmericanBlacks.

FIG. 26 is an exemplary profile cross-section of an exemplary lateralcondyle prosthetic showing how the measurements of c1-c4 translate intothe curvature of a prosthetic device fabricated in accordance with theinstant disclosure.

FIG. 27 is a 3D representation showing the outermost camming surfacepaths of the lateral and medial condyles for an exemplary distal femur,as well as the innermost path of the trochlear groove, in addition tothe arcuate profiling of the lateral and medial condyles and thetrochlear groove.

FIG. 28 is the 3D representation of FIG. 22 overlaid onto a 3D bonemodel of a natural femur.

FIG. 29 is a magnified view of FIG. 23 showing the distal portion of thefemur and the overlaid 3D representation.

FIG. 30 is a perspective view of a distal portion of a femur includingan exemplary 3D representation of the surface.

FIG. 31 is the mathematical representation of the curvature displayed inFIG. 24.

FIG. 32A is a graphical image plotting the ratio of the medial andlateral condyles to one another for 0-30 degrees.

FIG. 32B is a graphical image plotting the ratio of the medial andlateral condyles to one another for 40-70 degrees.

FIG. 32C is a graphical image plotting the ratio of the medial andlateral condyles to one another for 80-110 degrees.

FIG. 32D is a graphical image plotting the ratio of the medial andlateral condyles to one another for 120-150 degrees.

FIG. 33 is a proximal end of a tibia showing the axes, landmarks, andmeasurements taken in accordance with the instant disclosure.

FIG. 34A is an end view of a distal femur showing the trochlear path ofa typical Asian.

FIG. 34B is an end view of a distal femur showing the trochlear path ofa typical American White.

FIG. 34C is an end view of a distal femur showing the trochlear path ofa typical American Black.

FIG. 35 is a composite view showing the trochlear paths for a typicalAsian, American White, and American Black.

FIG. 36 is a composite profile view showing the shape of trochlear pathsfor a typical Asian, American White, and American Black.

FIG. 37 is a distal view of a femur showing areas of maximum differencebetween an Asian and an American White.

FIG. 38 is a distal view of a femur showing areas of maximum differencebetween an American White and an American Black.

FIG. 39 is a elevated perspective view of a tibia showing areas ofmaximum difference between an American White and an American Black.

FIG. 40 is a proximal view of a tibia showing areas of maximumdifference between an Asian and an American White.

FIG. 41 is a diagram showing an exemplary process for restoring deformedor missing anatomy using C1/C2 ratio in accordance with the instantdisclosure.

FIG. 42 is an exemplary plot of AP height versus ML width.

FIG. 43 is a plot for determining the optimum number of clusters usingDunn's Index and modified Dunn's Index.

FIG. 44 is an alternative Dunn's Index Equation (ADI).

FIG. 45 is a collection of views depicting an exemplary approximation ofa tibial plateau using a series of contours normal to the principal axesof the medial and lateral plateaus.

FIG. 46 is an exemplary plot of AP height versus ML width.

FIG. 47 is a perspective view of an exemplary polyethylene implant.

FIG. 48 is a series of perspective views of an exemplary implant.

FIG. 49 is a perspective view of an exemplary implant.

FIG. 50 is a cross sectional view of an exemplary implant.

FIG. 51 is a perspective view of an exemplary implant.

FIG. 52 is an anterior view of exemplary femoral and tibial componentsfabricated to correspond to the anatomical shape of the patient's kneefor a cruciate retaining implant.

FIG. 53 is a cross-sectional view taken across the lateral condyle andcondyle receiver for exemplary femoral and tibial components fabricatedto correspond to the anatomical shape of the patient's knee for acruciate retaining implant.

FIG. 54 is a cross-sectional view taken across the medial condyle andcondyle receiver for exemplary femoral and tibial components fabricatedto correspond to the anatomical shape of the patient's knee for acruciate retaining implant.

FIG. 55 is a comparison showing the difference between the anatomicalimplants and existing functional implants.

FIG. 56 is a comparison showing the difference in the restoration of thecorrect ratio between the medial and lateral anterior portions of theknee.

FIGS. 57 and 58 show the profiles of many functional implants.

FIG. 59 is an exemplary shaded map showing the variation between AfricanAmerican and Caucasian populations, where less shading corresponds togreater differences, whereas more shading corresponds to lessdifferences.

FIG. 60 is an exemplary flow diagram for generating a patient specificimplant from the 3D bone model.

FIG. 61 is a depiction of the point cloud used to represent the surfaceof patient's bone and used to calculate bone cross sectional contours.

FIG. 62 is a depiction of updating parameterized implant constraintswith the patient specific contours at an early stage of creation of apatient specific implant.

FIG. 63 is a depiction showing sweeping contours to generate smootharticulating implant surfaces that are patient-specific in accordancewith the instant disclosure.

FIG. 64 is an exemplary process flow diagram for updating existinglegacy implant systems with anatomical friendly templates.

FIG. 65 is a depiction of an updated existing legacy implant system thatincorporates a more anatomically accurate patellar groove.

FIGS. 66A and 66B are exemplary listings of parameters used to describean exemplary femoral component designed in accordance with the instantdisclosure.

FIG. 67 is an exemplary flow chart describing a process of automaticallyupdating the template parameters and generating an implant CAD.

FIG. 68 is a distal femur shown with corresponding contact areas thatare highlighted.

FIG. 69 is a proximal tibia shown with corresponding contact areas thatare highlighted for between 0-40 degrees of knee flexion.

FIG. 70 is a proximal tibia shown with corresponding contact areas thatare highlighted for between 60-140 degrees of knee flexion.

FIG. 71 are overhead views of a tibia tray insert having been modifiedor redesigned to simulate or approximate normal knee kinematics.

FIG. 72 is a conventional PS knee implant having limited axial rotation.

FIG. 73 is an elevated perspective view of an exemplary knee prosthesisdesigned in accordance with the instant disclosure that provides forretention of the anterior cruciate ligament.

FIG. 74 is a frontal view of an exemplary knee prosthesis designed inaccordance with the instant disclosure for use after an anteriorcruciate ligament revision surgical procedure.

FIG. 75 (Table 1) lists important femur measurements means, standarddeviations, t-tests, and power test results for typical Asians, typicalAmerican Whites, and typical American Blacks.

FIG. 76 (Table 2) lists important tibia measurements—means, standarddeviations, t-tests, and power test results for typical Asians, typicalAmerican Whites, and typical American Blacks.

FIG. 77 (Table 3) lists percentage length change in anterior cruciateligament and posterior cruciate ligament with respect to knee flexionangle.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The exemplary embodiments of the present invention are described andillustrated below to encompass methods and devices for designingprosthetic knee implants and, more specifically, to devices and methodsfor designing knee implants that more closely track the biomechanics ofthe natural knee and the resulting implants themselves. Of course, itwill be apparent to those of ordinary skill in the art that thepreferred embodiments discussed below are exemplary in nature and may bereconfigured without departing from the scope and spirit of the presentinvention. However, for clarity and precision, the exemplary embodimentsas discussed below may include optional steps, methods, and featuresthat one of ordinary skill should recognize as not being a requisite tofall within the scope of the present invention.

The following are definitions that relate to axes, landmarks, andmeasurements with respect to the distal femur (see FIGS. 2-4). Thesedefinitions also govern the proper construction of these terms as usedin the instant disclosure.

Transepicondylar Axis (TEA)—This measurement is known in theanthropological literature as biepicondylar breadth. To compute theclinical transepicondylar axis (TEA), rough sets of vertices weremanually defined on an average femur on the most lateral prominence ofthe lateral epicondyle and the most medial prominence of the medialepicondyle. This step was only performed once, since vertices in theatlas femora are homologous. Using these rough sets of points, a searchregion of 10 mm radius was defined from the centroid of the rough setsof vertices on both the lateral and medial sides. Defining the vectorfrom each of these centroids then gives a rough direction for the TEA. Apair of points was selected by maximizing the distance in this roughdirection; these selected points form the endpoints of the TEAmeasurement (see FIG. 2).

Distal Anatomical Axis—The distal anatomical axis was defined bylocating the shaft centroids at the distal one-third and distalone-fifth of the overall femur length.

Central AP Axis (CAP)—Using the distal anatomical axis and the TEA, amutually perpendicular axis was defined with termini at the posterioraspect of the intercondylar notch and the most anterior portion of theintercondylar groove. The length of this axis is recorded as CAP (FIG.3).This axis is similar to ‘height of intercondylar notch’.

Femoral Saddle Point—A landmark located at the most distal extension ofthe intercondylar groove.

Knee Center (K)—Using the two endpoints of the CAP measurement and thefemoral saddle point, a plane is defined which bisects the femur intomedial and lateral sides. The intersection of this plane with the TEA isthe knee center, which forms the distal endpoint of the mechanical axis(MA) of the femur. The proximal endpoint of the MA is the center of thefemoral head (see proximal femur measurements below).

AP Direction—Using the MA and the TEA, a mutually perpendicular vectorwith its origin at the knee center is used to define theantero-posterior (AP) direction, resulting in a direction similar toWhiteside's line.

Anterior Medio-lateral Width (AML) and Posterior Medio-lateral Width(PML)—The AP direction was used to locate four landmarks: the mostanterior and posterior points on the medial and lateral condyles of thedistal femur. Connecting the two most anterior points gives ameasurement of anterior medio-lateral width (AML) along the trochlearline, while connecting the two most posterior points gives a measure ofposterior medio-lateral width (PML) measured along the posteriorcondylar axis (PCA) (see FIG. 2).

AP Length of Medial and Lateral Condyles (LAP and MAP)—Connecting thepairs of lateral and medial vertices defined above, respectively, givesthe AP length of the lateral condyle (LAP) and medial condyle (MAP) (seeFIG. 3).

Posterior Plane—A unique plane containing the endpoints of the PMLmeasurement, which is also parallel to the MA, was used to define theposterior plane.

Overall AP Length—The minimum distance between the prominences of thelateral anterior condyle and the posterior plane (see FIG. 3).

AP Angle—The angle of the AML vector relative to the posterior plane(see FIG. 3).

Distal Medial-lateral Length (DML)—The most distal aspects of the medialand lateral condyles were recorded using MA as a reference direction.The distance between these two landmarks was denoted as DML.

Posterior Angle (PA)—The angle between the vector connecting the DMLlength and the mean axis of the femur (see FIG. 4).

Condylar Twist Angle (CTA)—The angle between the TEA and PCA.

Patellar Groove Height (GH)—Calculated between the posterior aspect ofthe intercondylar notch and the midpoint between the two DML axis points(see FIG. 4).

Femoral Shaft Curvature (SC)—The radius of curvature of the femoral meanaxis.

End of Definitional Section

Referring to FIG. 11, a schematic overview of the exemplary knee designprocess 100 includes obtaining one or more electronic three dimensional(3D) bone representations 102 that are stored in an electronic database.For purposes of designing a total knee implant, in the case of totalknee arthroplasty, that will replace the distal portion of the femur,the proximal portion of the tibia, the cartilage therebetween, and atleast a portion of the patella, it is useful to have 3D bonerepresentations of the distal femur, the proximal tibia, and thepatella, as well as 3D jig representations utilized to prepare thefemur, tibia, and patella for accepting TKA orthopaedic components. Togenerate these 3D bone representations and 3D jig representations, apatient or cadaver may undergo a CT scan, a series of X-rays, an MRI,and/or ultrasound imaging. The images of the bones and soft tissues fromthese tests, and possibly interpolated aspects of bone or soft tissue,are utilized to construct one or more 3D bone representations and one ormore 3D jig representations.

The images from the foregoing tests are loaded into a computer for dataanalysis. As is known to those skilled in the art, an MRI creates aseries of 2D “slices” of the relevant portion of the human anatomy.These 2D slices may then be segmented and stacked upon one another tocreate a 3D model or representation of the human anatomy. To the extentMRI is used to construct the slices, the precision of the 3D modeldepends in part upon how “thick” the slices are from the MRI. Ananalogous process is utilized for CT scans, X-rays, and ultrasoundswhere the 2D images are taken from distinct points and utilized toconstruct a 3D model of the anatomical feature in question, forexemplary purposes only this anatomical feature in question is describedin the context of a human knee joint.

This same process for taking 2D images and using these images to createa 3D model is applicable to generating any 3D model of a human joint orbone(s). This same process may be applied to a living or dead humanbeing in order to generate a plurality of bone or joint models forfurther analysis. It should also be understood that these same 2D imagesare useful to construct 3D models of cartilage that may be selectivelyinterposed between bones, in exemplary form the femur and tibia, to moreaccurately depict the anatomy of each human feature (bone, joint, etc.).As will be discussed hereafter, the 3D models of the cartilage may beuseful in constructing the 3D jig models.

Referring to FIG. 12, a series of 3D distal femoral representations areshown. As will be discussed in more detail hereafter, the exemplary kneedesign process 100 may be utilized to design and construct a customizedknee implant that is unique to the anatomy of each patient. In addition,the exemplary knee design process 100 may be utilized to design andconstruct one or more generic implants that may be utilized toapproximate the anatomies of larger populations where customizationcosts are not commercially feasible or preferable.

Referring back to FIG. 11, after one or more bones have been modeled sothat 3D representations, in electronic form, have been generated, the 3Drepresentations are stored in a database 104 that correlates additionaldata with the 3D representations. In exemplary form, the database 104also includes data specific to each 3D representation in order toclassify the representation including, without limitation, age, gender,race, and height of the human from which the bones, joint, etc., werescanned. At the same time, each 3D representation may include a grade orevaluation as to the condition of the bone, joint, etc. In exemplaryform, when a 3D depiction of a knee joint (at least the proximal tibiaand distal femur) is saved in the database 104, classifications forcartilage wear, bone degeneration, and osteophyte growth can beidentified.

Referring to FIGS. 13 and 14, subsequent to the generation of eachindividual bone model, the exemplary process 100 includes generation ofa 3D model of the knee joint 300. This 3D model 300 of the knee jointincludes orienting the distal femur 302, proximal tibia 304, and patella306 as each would be when the joint was in full extension. Thereafter,computer software is operative to reposition the bones of the 3D modelto create a virtual range of motion for the knee joint through fullflexion. At the same time, the 3D models 300 may include cartilage (notshown) that interposes the bones 302, 304, 306 to represent the naturalcartilage that cooperates with the proximal end of the tibia 304 to formmedial and lateral condyle receivers.

101391 Referencing FIGS. 15 and 16, the 3D joint model 300 is useful togenerate 2D contact profiles or “slices” showing how the orientation ofeach slice changes as knee joint is taken through its range of motion.In particular, these 2D representations are useful in understanding thata prosthetic implant, just like a natural knee, can be thought of as aseries of slices that combine and work together to form the entirejoint. As a result, by evaluating and understanding the geometry of eachslice, specific contours may be seen that will be unique to each patientor may be generalized over a more encompassing population. It should benoted that the 3D joint model 300 may incorporate different topographiesdepending upon ethnicity, gender, and/or age. These differingtopographies result in differing slices.

Referring to FIGS. 17-20, after each 3D model 300 has been generated andsaved, a series of radii of curvature measurements are taken for boththe medial and lateral condyles 308, 310 associated with each 3D model.In exemplary form, a distal femoral 3D model includes correspondingmedial and lateral condyles 308, 310 separated by a trochlear groove312. Each lateral and medial condyle 308, 310 includes a camming surfacehaving points along the camming surface that are farthest away from thecenter of the bone as the femur rotates through its range of motion. Inorder to calculate medial profile, a plane defined by the medialanterior point (most anterior point in medial condyle), the medialdistal point (most distal point on medial condyle) and the medialposterior point (most posterior point in medial condyle) is intersectedwith the distal femora this results in contour that corresponds to themost protruding points on medial condyle surface, the same method isused to calculate the lateral profile as shown in FIGS. 17, 19 and 20.These 3D paths are then converted to a single best-fit path within oneplane for each condyle.

For the sulcus profile calculation, a set of contours is extracted byintersecting the distal femur with a series of planes rotating aroundthe transepicondylar axis with a 10 degree increment. The lowest pointson these contours are then used to define the sulcus points as shown inFIG. 19.

A similar procedure is utilized to generate a set of points along a 3Dpath of the trochlear groove using the points along the surface that areclosest to the center of the bone as the femur rotates through its rangeof motion. These closest points (i.e., lowest portion of the trough) areshown in FIGS. 19 and 20. This 3D path is then converted to a singlebest-fit path within one plane (as shown in FIGS. 19 and 20).

Referring to FIGS. 21 and 22, the inventors of the present inventionhave found that the shape of the 2D paths for both the medial andlateral condyle bearing surfaces, as well as the 2D path for thetrochlear groove, are important in attempting to design a prostheticfemoral component that closely resembles the natural shape of the distalfemur. In order to generate specific sizing and curvature measurementsfor generation of the femoral component, the inventors have found thatapplication of four radii of curvature to each femoral condyleaccurately resembles the curvature of the natural femur condyles.

Referencing FIGS. 23-25, FIG. 23 is a composite view of the lateral andmedial femoral condyles for the Whites, Blacks, and Asians, whereas FIG.24 shows the medial profile for a medial femoral condyle for Whites,Blacks, and Asians, and FIG. 25 shows the lateral profile for a lateralfemoral condyle for Whites, Blacks, and Asians.

Referring back to FIGS. 6 and 21, as well as FIG. 26, each path for theoutermost medial condyle camming surface and the outermost lateralcondyle camming surface is segmented into four zones. It has beenidentified by the inventors that the curvature of each of these zonescan be approximated by the curvature of a circle. In other words, eachzone has a curvature that approximates the constant arc of a circle. Forexample, the first zone has a radius of curvature, identified as c1.Simply put, this c1 value is the radius of a circle that most closelyapproximates the curvature of this portion of the camming surface 2Dpath, which is the most posterior portion of the path. The second zone,immediately adjacent to the first zone, has a radius of curvature of c2.Again, this c2 value is the radius of a circle that most closelyapproximates the curvature of this second zone. The third zone followsthe second zone and also includes a radius of curvature, c3. Finally,the fourth zone, which approximates the contour of the anterior portionof each of the respective condyles, has a radius of curvature of c4.

In the circumstances where a series of knee joints are electronicallymodeled from X-rays, CT scans, MRIs, etc., a comparison may be carriedout to discern how the radii of curvature vary within each zone andacross all zones. The chart in FIG. 21 is derived from actual 3D bonemodels derived from human X-rays, CT scans, MRIs, and/or ultrasounds.This chart includes mean radii of curvature in metric units (incentimeters) for each zone based upon gender. In addition to giving themean radius of curvature for each zone, the table also represents thestandard deviation for each zone to provide a quick comparison betweenthe zones for the lateral and medial condyles.

Referring back to FIGS. 22 and 26, a profile view of a human knee jointremoves the distal portion of the femur and replaces it with circlescorresponding to the radii of curvature for each of the four zones(c1-c4) for both the medial and lateral condyles. This figure provides arepresentative view of what radii of curvature represent in terms of arcand the relative sizes of the circles in relation to the adjacentanatomical features of the distal femur. As will be discussed hereafter,these circles are relevant in attempting to approximate the curvature ofa native distal femur in a prosthetic implant. The locations of thecenters of the circles may be used inside an exemplary model. They maybe calculated using linear square fitting of a circle in each set ofcurve points, which gives radii and centers of best approximatingcircles for the curves.

Referring to FIGS. 27-32, as discussed above, 3D paths are created thattrack the outermost camming points throughout the range of motion forboth the medial and lateral condyles, as well as the innermost pointsthroughout the range of motion of the trochlear groove. Each outermostcamming path is utilized in conjunction with the path for the trochleargroove to mathematically map the topography of both condyles and thetrochlear groove. Curvature of the medial, lateral and sulcus profilesare then calculated by finding best number of circles passing thataccurately approximate the curve as shown in FIG. 27. To capture thecurvature of the condylar surface, the curves produced earlier byintersecting the femur with the planes around TEA are trimmed around themedial, lateral and sulcus profiles, the circle of curvature of each ofthese trimmed contours are then calculated as shown in FIG. 27.

Each outermost condyle camming path, in addition to the trochlear groovetrough path, is divided into variable degree increments along the rangeof motion of the distal femur as it rotates with respect to the tibia.In the images provided, ten degree increments were used, although otherincrements are within the scope of the disclosure (e.g., 5-15 degreeincrements may be employed in some exemplary embodiments). The length ofeach path is divided into ten degree increments, with a curve beingapplied at the boundary of each increment. A separate medial-lateralcurve is applied to the widthwise portion (medial to lateral) of eachcondyle and the trochlear groove at each ten degree increment. The archof each separate medial-lateral curve is chosen to most closelyapproximate the medial-lateral curvature at each point along therespective paths. Thereafter, a radius of curvature is determined foreach medial-lateral curve.

Referring to FIG. 33, the following landmarks and measurements wereidentified automatically for the distal femur:

-   -   1) Intercondylar Eminence Points The two highest projecting        points on the medial and lateral intercondylar eminences.    -   2) Eminence Midpoint The midpoint between the lateral and medial        intercondylar eminence points.    -   3) Tibial Tuberosity—The most anteriorly protruding point on the        tibial tuberosity.    -   4) ML—Maximum width of the tibia plateau in the medial-lateral        direction.    -   5) AP—Length of the tibial plateau in the anterior-posterior        (AP) direction and passing through the midpoint of the tibial        intercondylar eminence (i.e. eminence midpoint).    -   6) Eminence Width (EW)—Distance between medial and lateral        intercondylar eminence points.    -   7) Tibial Twist Angle (TTA)—Angle between the AP direction and a        line connecting the intercondylar eminence midpoint and tibial        tuberosity.    -   8) Lateral Plateau Height (LPH)—Length of the lateral tibial        plateau in the AP direction.    -   9) Lateral Plateau Width (LPW)—Length of the lateral tibial        plateau in the ML direction.    -   10) Medial Plateau Height (MPH)—Length of the medial tibial        plateau in the AP direction.    -   11) Medial Plateau Width (MPW)—Length of the medial tibial        plateau in the ML direction.    -   12) Eminence ML Ratio (EMLR)—Ratio of MPW (i.e. medial plateau        width) over ML.    -   13) Maximum Length—Length of the tibia from the medial malleolus        to the intercondylar eminence.

Referring to FIGS. 34A-36, it can be seen that the trochlear groove fordifferent ethnicities has a different shape and path. FIG. 34Arepresents the trochlear groove path for a typical Asian, while FIG. 34Brepresents the trochlear groove path for a typical American White, whileFIG. 34C represents the trochlear groove path for a typical AmericanBlack. In addition, FIG. 35 provides a composite view of the trochleargroove path for a typical Asian, a typical American White, and a typicalAmerican Black. Finally, FIG. 36 provides a profile view showing how theshape of the trochlear groove also varies among Asians, American Whites,and American Blacks. The results from the feature finder shape analysistool, as described above, highlight shape differences in the femoralshaft, lateral condyle, and greater trochanter, in addition to thedistal femur.

Referring to Table 1 and FIGS. 37-40, the results from the t-tests andpower tests for the automated measurements. In American Blacks, thelateral condyle has higher AP height (p<0.01) whereas the medial condyleheight wasn't significant , thereby creating a more trapezoidal-shapedknee as opposed to the more square-shaped knee in American Whites whichresulted in larger AP condyle angle in American blacks. On the otherhand, our analysis performed on the distal femur of the East Asianpopulation identified a distinct pattern in the AP and ML where the APand ML measurements are smaller in the East Asian population as comparedto both the Caucasian and African American populations (p<0.01). Ingeneral, the Asian population exhibits a more trapezoidal shape than theCaucasian and African American populations (p<0.01). In addition, theEast Asian population also has a narrower anterior width (p<0.01).

Analyzing the curvature of both lateral and medial profiles it has beenfound that they can be accurately approximated by four distinct radii ofcurvature for American black and American white and three distinct radiifor East Asians (see FIG. 6). These four radii were found to beconsistent between both ethnicities (American Black and American White),however the value of these radii were different in each ethnicity asshown in FIGS. 23-25.

The feature finder results for the tibia indicate that ethnic shapedifferences between American white and American black are not assignificant at the medial and lateral plateau areas as opposed to moreshape differences around tibial tuberocity area. Besides minordifferences in the proximal anterior tibia, the only area thatregistered significant was the tip of the medial malleolus (see FIGS. 39and 40). However, a major shape difference was found between East Asianpopulation and both American White and American Black (FIGS. 23-35). Theresults from the t-tests and power test underscore these findings, aswell. The most significant variables are those related to scale,including maximum length, measures of shaft robusticity, and severalmeasurements of the tibial plateau. In short, American Black tibiae arelonger with a more robust shaft and slightly larger tibial plateau.

Table 2 shows the automated measurements for the tibia with lateralplateau height as the most significant measurement (p<0.05) whichcorrelates to the significant difference in the lateral femoral condyleheight.

Referring back to FIG. 31, the radii of curvature for the medial-lateralcurves are determined for both the medial condyle and the lateralcondyle at each ten degree increment, from posterior to anterior. Thefirst column is structured in ten degree increments along eachoutwardmost camming surface path for both the medial and the lateralcondyles. The second and third columns refer to the radius of curvaturefor the medial and lateral condyles at the respective angle increments.The final two columns are ratios corresponding to the curvature of themedial-lateral radius of curvature divided by the radius of curvaturefor the respective camming surface paths. In other words, the ratio hasa numerator that is the radius of curvature from side to side of eachcondyle, and a denominator that is the radius of curvature for the zone(which is the same number for a zone) along the path of the outermostcamming surface of each condyle. This ratio is then plotted for eachzone, for various planes taken at specific angles with respect to themechanical axis (MA).

Referring to FIG. 41, the ratio of C1/C2 (see FIG. 29) can be used torestore deformed anatomy to generate a smooth articulating surface ofpatient specific implant. The process may begin by calculating lateraland medial profile and the curves for the condylar surface for thepatient as outlined in the previous point, these contours are thenevaluated to verify that the curvature of each sectional curve is withinthe normal anatomical range. Deformed sections are then highlighted andC1/C2 ratios are calculated for the anatomical correct sections, thesesections are then used to interpolate the ratio for the deformedsection, upon completion of this process a smooth implant articulatingcurvature that mimics the patient correct anatomy is generated.

The results are utilized to approximate the radii of curvature along thecondyles, C2, when abnormalities exist within the bone. A relationshipbetween ratios of C1 and C2 for the medial and lateral condyles has beenidentified and can be used calculated the radius of curvature for aspecific location along either condyle, C2.

Using the radii of curvature for the outermost camming surface paths forthe medial and lateral condyles, as well as the mapping of the curvaturefor the medial-lateral arcs, a novel prosthetic implant may befabricated that is patient specific. At each degree increment, a smoothcurve is generated using the radii of curvature and three points alongthe medial condyle, trochlear groove, and lateral condyle (see FIG. 29).The articular surface of the implant is then approximated using a sweepsurface of these smooth curves.

Referring to FIGS. 41 and 26, four distinct radii of curvature have beenidentified for the outermost camming surface of the lateral and medialcondyles.

Referring to FIG. 42-44, six cutting box sizes were identified byanalyzing the aspect ratio between the anterior-posterior height and MLWidth. The AP height is defined as the distance between the sizing pointand most posterior point on the femur while the ML width is defined asthe size of the femur in the medial lateral dimension. This aspect ratioare then calculated for all population this ratio along with and notlimited to features highlighted in table I are then used as amultidimensional feature vector to cluster the population, best numberof clusters are determined using both Dunn's Index and alternativeDunn's Index (see FIGS. 43 and 44) which arc used to identify of howcompact and well separated the clusters are. In exemplary form, twelveclusters were found that best represent the American White populationwhich are divided into six clusters for males and six for females)

Referring to FIG. 45, the tibial plateau is approximated using a seriesof contours normal to the principal axis of the medial and lateralplateau. These contours arc used to parameterize the surface of thepolyethylene for the tibial implant.

Referring to FIG. 46, six tibial plate sizes were identified bymeasuring the length of the tibial surface in the anterior-posteriordirection and measuring the tibia length in the medial-lateraldirection. The ratio between these two measurements was then clusteredusing fuzzy c-means to identify six sizes the best fit the population.

Referring to FIG. 47-51, the polyethylene reflects the anatomical shapeof the tibial plateau for a cruciate retaining implant (see FIG. 47) andfor a bi-cruciate implant (see FIGS. 48-51). The polyethylene can alsobe modular and may include medial and lateral polyethylene inserts whichpreserve the tibial eminence. A connector is used (FIG. 39) to ensurethe accurate placement of the inserts. Once secured, the connector isremoved leaving only the medial and lateral polyethylene inserts andtibial trays in place (FIG. 51).

Referring to FIGS. 52-54, the femoral and tibial components of theimplant corresponding to the anatomical shape of the knee showing thecurvature matching between the two components radii.

Referring to FIGS. 55-58, a comparison shows the difference between theanatomical implants and existing functional implants. FIG. 55 shows thedifference in the restoration of the correct ratio between the medialand lateral anterior portions of the knee. Existing functional implant(blue) does not properly restore this ratio causing more tension alongthe quadriceps which can alter the motion of the knee and can causesublaxation of the patella. FIGS. 56-58 show the curvature of the medialand lateral profiles for the anatomical implant as compared to existingfunctional implants. FIG. 56 illustrates a direct comparison to atypical implant, whereas FIGS. 57 and 58 shows the profiles of manyfunctional implants.

Referring to FIG. 59, the color map shows the variation between AfricanAmerican and Caucasian populations. The brighter colors show higherdifferences than darker colors. Little variation exists on the distalend of the femur although the lateral condyle does show slightdifferences.

An exemplary process of selecting a template that best fit patientanatomy can be described as following. A patient knee will first beimaged and a 3D surface of the patient femur and tibia will begenerated. The femoral bone is then analyzed to calculate the medial andlateral camming paths. Medial and lateral sagital curves are thencalculated. Anterior posterior size and medial lateral size of the femurare also calculated. The curvature of the camming paths along with thesagital curves, AP size and/or medial lateral width may be used tolocate the best template that fit the patient. For patients whereimplant template doesn't fit their anatomy, a custom implant isgenerated as shown by the right branch of FIG. 11.

Referring to FIG. 60, an exemplary process for generating a patientspecific implant from any imaging modality includes generating threedimensional patient specific models, these models are then added to theforegoing discussed (DAT) statistical atlas to achieve pointcorrespondence and normalization, upon completion of this processrelevant surgical landmarks are automatically calculated (TEA, MA, PCA,. . . etc).

Referencing FIGS. 61-63, a rotating plane around the TEA is then used tocalculate bone cross sectional contours (see FIG. 61) and another set ofcontours normal to the MA are then calculated (see FIG. 62). These twosets of contours arc then used to update the constraints of theparameterized implant template automatically, upon updating of theseconstraints, the implant articulating surface is then swept to generatea smooth continuous surface (see FIG. 63). Measurements of theanterior-posterior height and medial-lateral width from the patient'sbone are also used to update a template cutting box. This box is thencombined with the smooth articulating surface to generate a patientspecific implant CAD model. This implant 3D CAD model is then evaluatedagainst the 3D model of the patient specific bone to verify theplacement and a simulation of range of motion is performed with the 3Dimplant model and the 3D bone model. Upon completion of the verificationprocess, the 3D implant model is output from a computer to amanufacturing facility in order to manufacture the implant. In exemplaryform, the computer output of the 3D implant model may be in the form ofG-code for a CNC machine.

Referring to FIG. 64, an exemplary flow chart outlines how implanttemplates generated from the clusters that best fit the population canalso be used to update existing legacy systems to ensure conformity withthe patient's anatomical trends. This process involves importing a CADmodel of an existing implant system and transforming it to sameparameterization space as the anatomical templates. This processincludes generating a set of three dimensional contours around theimplant mid axis. These contours are used to generate a set ofconstraints in same manner as the anatomical templates. Once the implantis parameterized just as are the templates, the templates parametervalues are used to update the parameterized implant features. Theseparameterized implant features include, but are not limited to, patellargroove curvature, condylar curvature, AP height, and ML width.

FIG. 65 shows how anatomical friendly templates can be used to updateexisting implant families to create an implant that mimics an anatomicalpatellar groove.

Referring to FIGS. 66A-66B and 67, an exemplary parametric femoral CADmodel consists of 300+ parameters. The CAD model is defined by crosssections around the TEA axis at 10 degrees increment. The parametersdefine specific points and curvatures of each cross section. Thepatella-femoral section of the implant is defined by three points fromthe medial, lateral, and groove curvatures along with 3 radii, as hasbeen previously discussed. As for the condylar cross sections, themedial side and lateral side are defined by two points and a singleradius. Shaping information is inherent within the cross-sections inorder to create a full implant CAD model automatically.

Referring to FIG. 68-70, in order to design a functional implant thatbest mimics the normal knee motion, the full range of the femur relativeto the tibia should be completely characterized. To achieve this goal, aset of anatomical areas are localized on the femur and projected on thetibia during the full range of motion. First, the most distal area onthe medial side of the femur was localized, which is the area of contactbetween the femur and tibia in case of full extension (A1) (see FIG.69). The second area is the most distal area of the lateral condyle(A2), while the third area is the most posterior area of the medialcondyle (A3) and the fourth area is the most posterior area of thelateral condyle (A4) (see FIG. 70). During the full range of motion,each of the areas on the femur was projected on the tibia tocharacterize the motion of these areas relative to the tibial plateausurface. A distinct motion pattern is observed on the medial side wherearea A1 moves anteriorly until 40 degrees flexion and then disengagesfrom any contact with the tibia surface. At the same time after 40degrees, the area A3 starts to move anteriorly while performing axialrotation tracking. On the lateral side, the area A2 moves anteriorlywith less magnitude compared to A1 until 40 degrees flexion, where itdisengages in a similar fashion as A1. At the same time, area A4 comesin contact with and moves anteriorly in a smaller area compared to areaA3.

Referring to FIGS. 68-72, in order to achieve the normal motion patternwith a functional PS implant, the design of both the femoral implantcurvature and the polyethylene component should be modified to provide amore natural motion. In addition, modifying the cam location on thepolyethylene component provides constraint for the femur motion andallows for more axial rotation (see FIG. 71). None of the existingfunctional implants is operative to provide the same axial rotation asis observed in the normal knee. When a PS implant (see, e.g., FIG. 72)was implanted and thereafter X-ray fluoroscopy studies were carried outto observe the location of the femoral component relative to the cam, itwas observed that the cam position intruded into the femoral implant,thereby implying that the cam location does not allow for sufficientaxial rotation. In order to improve the axial rotation of the implantjoint, the cam position was modified to tilt laterally according to theloci on the medial side. This modification allowed for a better range ofaxial rotation, which more closely approximated the normal range ofmotion of a natural knee joint.

As seen in FIGS. 69 and 70, the lateral side of the tibia has twodistinct loci. The lateral curvatures of the PS polyethylene in FIG. 71arc designed to accommodate such unique conditions. During the flexionfrom 0 to 40 degrees, the anterior portion of the polyethylene componentis defined by four sets of curvatures. This geometry also angles toprevent excessive anterior sliding of the femoral component during theseflexion angles. The posterior portion of the polyethylene component isalso defined by four sets of curvatures, which engage the lateralcondyle from 60 to 140 degrees of flexion. This portion is designed tobe flatter to provide smoother motion and prevent impingements. Themedial side has one set of curvature that is shaped as a deep dish forthe rolling motion during the 60 to 140 degrees of flexion. A second setof curvatures introduce a unique track that first follow the loci from60 to 120 degrees of flexion and blends into the loci from 0 to 40degrees of flexion, which allows for a smooth transition between the twoloci tracks.

Referring to FIGS. 73-74 and Table 3, in order to design anatomicallyfriendly bicruicate, ACL, and PCL implants, the location of the PCL andthe ACL should be studied as the knee joint is taken through its rangeof motion. A statistical atlas was utilized to localize and propagatethe location of insertions of the ACL and the PCL across an entirepopulation. Both the ACL and PCL were deformed by taking the knee jointthrough a range of motion in order to map the change in shape and lengthof the ligament during range of motion. Table 3 highlights thedifferences in length of the ACL and the PCL as percentage of the ACLlength. Using this data, an implant may be designed to accommodateretention of either the PCL or the ACL or both the ACL and PCL.

Following from the above description and invention summaries, it shouldbe apparent to those of ordinary skill in the art that, while themethods and apparatuses herein described constitute exemplaryembodiments of the present invention, the invention contained herein isnot limited to this precise embodiment and that changes may be made tosuch embodiments without departing from the scope of the invention asdefined by the claims. Additionally, it is to be understood that theinvention is defined by the claims and it is not intended that anylimitations or elements describing the exemplary embodiments set forthherein are to be incorporated into the interpretation of any claimelement unless such limitation or element is explicitly stated.Likewise, it is to be understood that it is not necessary to meet any orall of the identified advantages or objects of the invention disclosedherein in order to fall within the scope of any claims, since theinvention is defined by the claims and since inherent and/or unforeseenadvantages of the present invention may exist even though they may nothave been explicitly discussed herein.

What is claimed is:
 1. A method for generating a patient-specificprosthetic implant, the method comprising: generating, using one or moreprocessors and from a medical image of a human anatomical feature, athree-dimensional electronic representation of the human anatomicalfeature including size and surface-curvature features matching the humananatomical feature, the surface-curvature features including one or moreradii of curvature on an outer camming surface of the human anatomicalfeature; selecting, using the one or more processors, a virtual implanttemplate from a database of virtual implant templates; designing, usingthe one or more processors and based on the selected virtual implanttemplate, a patient-specific prosthetic implant to imitate the size andsurface-curvature features of the three-dimensional electronicrepresentation; and testing virtually, using the one or more processors,fit of the patient-specific prosthetic implant using thethree-dimensional electronic representation of the human anatomicalfeature.
 2. The method of claim 1, further comprising forming thedatabase of the virtual implant templates by generating, using the oneor more processors, a series of the virtual implant templates,including: generating, using the one or more processors, a plurality ofelectronic three-dimensional models representing said human anatomicalfeature across a population of humans; grouping the plurality of modelsin a database; associating each of the plurality of models in thedatabase at least one characteristic selected from the group consistingof: age, race, and gender; and designing, using the one or moreprocessors, said plurality of virtual implant templates, where each ofthe plurality of virtual implant templates corresponds to at least aportion of the population of humans for which electronicthree-dimensional models were generated.
 3. The method of claim 2,wherein designing said plurality of virtual implant templates includes,for each of at least a portion of the plurality of virtual implanttemplates, incorporating a size and/or a contour that approximates amean size and/or a mean contour, respectively, of at least thecorresponding portion of the population of humans.
 4. The method ofclaim 2, further comprising virtually test fitting, using the one ormore processors, at least one of the plurality of virtual implanttemplates to at least one of the plurality of electronicthree-dimensional model.
 5. The method of claim 2, further comprisingmeasuring, for at least two of the plurality of electronicthree-dimensional models, at least one topography selected from thegroup consisting of: a medial condyle camming surface topography, alateral condyle surface topography, and a trochlear groove topography.6. The method of claim 1, wherein the human anatomical feature is afemur, and the method further comprises identifying one or morerepresentative surface-curvature features on the three-dimensionalelectronic representation by: generating a shell of the femur from bonemapping, generating profiles/points from the shell by sweeping aroundthe bone every ten degrees, generating a curve from the profiles/points,and matching at least four radii to the curve.
 7. The method of claim 1,where the human anatomical feature for which the three-dimensionalelectronic representation is generated is a human anatomical feature,and generating the three-dimensional electronic representation of thehuman anatomical feature further comprises: imaging at least a portionof the human anatomical feature; creating, using the one or moreprocessors, a plurality of 2D image slices of the human anatomicalfeature taken orthogonal to an axis extending through the humananatomical feature, where each of the plurality of 2D image slicesincludes a bone segment comprising an enclosed boundary corresponding toan exterior of the patient's bone; and constructing, using the one ormore processors, a 3D image bone shell of at least the portion of thehuman anatomical feature for which the plurality of 2D image slices weretaken.
 8. The method of claim 7, wherein constructing the 3D image boneshell further includes using software to recognize the enclosed boundaryof each bone segment by using a template 3D image bone shell that is notpatient-specific, and where the 3D image bone shell depicts a currentstate of the patient's human anatomical feature.
 9. The method of claim7, wherein the imaging comprises at least one of magnetic resonanceimaging and computed tomography.
 10. The method of claim 7, wherein thepatient's bone comprises at least one bone selected from the groupconsisting of: a femur, a tibia, and a humerus.
 11. The method of claim7, further comprising generating, using the one or more processors and asoftware component running on the one or more processors, a 3D imagesurgical jig configured to mate with the 3D image bone shell, where the3D image surgical jig includes topographical features customized to theexterior features of the 3D image bone shell.
 12. The method of claim11, wherein the software component is operative to output an instructionfile for fabricating a surgical jig having tangible topographicalfeatures of the 3D image surgical jig.
 13. The method of claim 7,further comprising virtually constructing, using the one or moreprocessors, a 3D image cartilage shell representing at least a portionof a patient's cartilage using the plurality of 2D image slices of thethe human anatomical feature, where constructing the 3D image cartilageshell includes using software to recognize an outline of cartilageappearing in a 2D image slice.
 14. The method of claim 1, furthercomprising sweeping, using the one or more processors, the selectedvirtual implant template, after the step of associating, to create asmooth articulating surface template.
 15. The method of claim 14,further comprising generating, using the one or more processors, avirtual template cutting guide representing the cuts to be made to ahuman bone to adapt the human bone to accept the patient-specificprosthetic implant.
 16. The method of claim 15, further comprisingmerging, using the one or more processors, the virtual template cuttingguide and the smooth articulating surface template to generate a patientspecific virtual model, wherein the patient specific virtual model isused to generate the patient-specific prosthetic implant.
 17. The methodof claim 15, wherein generating a virtual template cutting guideincludes automatically measuring an anterior-to-posterior height and amedial-to-lateral width of the three-dimensional electronicrepresentation of the human anatomical feature.
 18. The method of claim15, wherein generating a virtual template cutting guide includesautomatically measuring an anterior-to-posterior height and amedial-to-lateral width of the three-dimensional electronicrepresentation of the human anatomical feature.
 19. The method of claim18, further comprising merging, using the one or more processors, thevirtual template cutting guide and the smooth articulating surfacetemplate to generate a patient-specific virtual model used to generatethe patient specific prosthetic implant.
 20. The method of claim 18,wherein generating a virtual template cutting guide includesautomatically measuring an anterior-to-posterior height and amedial-to-lateral width of the three-dimensional electronicrepresentation of the human anatomical feature.
 21. The method of claim1, wherein the human anatomical feature is a femoral component of a kneejoint, the camming surface includes an anterior-to-distal-to-posteriorsurface of the medial or lateral condyle, and the method furthercomprises identifying at least three radii of curvature on the cammingsurface of the femoral component that are obliquely angled to amedial-lateral direction of the femoral component.
 22. The method ofclaim 1, wherein the human anatomical feature is a femoral component ofa knee joint having a trochlear groove surface that includes ananterior-to-distal surface incorporating at least two radii of curvatureobtusely angled to a medial-lateral direction of the femoral component.23. The method of claim 1, wherein the human anatomical feature is afemoral component of a knee joint having a trochlear groove surface thatincludes a medial-to-lateral surface incorporating at least two radii ofcurvature parallel to a medial-lateral direction of the femoralcomponent.
 24. The method of claim 1, further comprising generating thepatient specific prosthetic implant using the selected one of thevirtual implant templates.